A sounding line or lead line is a length of thin
rope with a
plummet, generally of
lead at its end. No matter what metal the plummet is made of, it's still referred to as "the lead."In the recent past, depths were measured in
fathoms, although since
metrication this has mostly changed to
metres. Most US charts use fathoms, occasionally feet. Sounding lines were widely used in
navigation until the development of
ultrasonic depth measuring devices. The sounding line has been superseded by
echo sounding. These can be cheap, accurate and provided a real-time graphical profile of the depth of the seabed. To work continuously and reliably, they do need
electrical power and shelter from rain and spray, something that can be difficult to maintain on smaller and open
boats.
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